Molecular and morphological perspectives on the circumscription of Carex section Heleoglochin (Cyperaceae)
Vignea is the only monophyletic subgenus in the genus Carex (Cyperaceae), comprising nearly 300 members grouped into 19–28 sections. Molecular studies have demonstrated that most of these sections are polyphyletic. Here, we seek to clarify the relationships among species in section Heleoglochin based on phylogenetic and morphological analyses. We analyzed sequence data using nuclear ribosomal DNA internal and external transcriber spacer regions of 60 representative specimens of sect. Heleoglochin, representing the full geographic range of the section and of species that are themselves geographically widespread. We used maximum likelihood and Bayesian inference to estimate phylogeny and divergence times based on molecular data. We scored 17 vegetative and inflorescence characters on 303 specimens and 23 perigynium characters on 56 specimens to characterize morphological variation within and among species and clades. We undertook a comparative analysis of morphological, molecular, and biogeographic patterns to evaluate sectional limits and relationships. Our findings confirm that section Heleoglochin is polyphyletic, with three main lineages—Eurasiatic, North American, and Oceanic clades—supported by molecular, morphological, and biogeographic data. Morphological and molecular analyses support two disjunctures: the European species Carex appropinquata appears sister to the Oceanic lineage, and all the specimens of C. diandra distributed worldwide are grouped together in the North American clade. Concordance among morphological, molecular, and biogeographic data supports each of the lineages and highlights the potential of integrative studies to illuminate the causes of mismatches between phylogeny and traditional classifications. Such integrative studies are needed to make headway on the systematics of this thorny genus, in which non-monophyly of traditional sections is the rule rather than the exception.